Shortwave listening and everything radio including reviews, broadcasting, ham radio, field operation, DXing, maker kits, travel, emergency gear, events, and more
In that section of the RadioReference Wiki, written by Mike, KA3JJZ, I found the following:
Another way an active preselector could be used is to use it to load a very short dipole – say not more than 1 meter (roughly 3 foot) for each leg. A number of years ago, a company called Datong marketed such an antenna (with a preamp right at the antenna feedpoint) that was popular in Europe and to some lesser extent in the Americas because it’s easy to hide the antenna.
In the magic of my mind, I could picture using the short dipole strung across two windows — or a large window — in an apartment or condo (or anyplace with antenna restrictions) and connected to an MFJ 1020C. I had not yet done the experiment, but I had tested the 1020C and found it to be a worthy piece of gear. So I thought the short dipole/1020C experiment might be worth a shot.
The heart of the short dipole, the LDG 9:1 unun.
So I cut two yard-long lengths of wire and attached them to a 9:1 unun. I created loops at the outer end of each leg of the dipole and hung the whole assembly from a curtain rod covering two windows. A coax links the short dipole to the MFJ 1020C, and a jumper connects the output of the 1020C to my Satellit 800 receiver.
The completed dipole. Not fancy, but it works.
Bottom line: it works. The vast majority of the time, even when the 1020C preselector is in bypass mode, the short horizontal dipole/1020C combo delivers a better signal-to-noise than the Satellit’s vertical telescopic antenna. (In rare cases, they are equal.) And when the preselector amplification circuits are activated and properly tuned, the signal is usually improved, often significantly. The Big Trick is to use the preselector to peak the noise at the frequency you want to hears and then tune slightly to the side of best listening.
Obviously that would be cumbersome for band-scanning, but you could band-scan in bypass mode and then tweak the “hits” with the amplification circuitry. In all, if you are living in an antenna-challenged situation, the short dipole/1020C combo just might make your shortwave listening better.
Final thought: Mike, who wrote the section of Radio Reference wiki that inspired this experiment, said:
You do have to watch your gain otherwise you will get a lot more noise than signal. I did my experiment using an old Palomar preselector. You can also try using a YouLoop as the antenna – it should, in theory, work even better than just a simple whip.
One thing that you could mention in your article is that there is an advantage to having a small dipole like that as the receiving element. Not only is it fairly easy to hide, it can be moved around to find a somewhat quieter location. However the coax should be kept as short as you can, otherwise there is a chance that common mode noise would become an issue – particularly if it runs near computers or other RFI sources
Remember that even a 1 or 2 S unit improvement might make the difference between hearing a signal and not hearing it at all. All we are doing here is trying to improve the signal/noise ratio coming into the unit. That little vertical whip on the 1020c is not likely to be the best choice, and that’s what I am trying to improve upon.
A few weeks ago, Chameleon Antenna sent me a pre-production model of their new wideband magnetic loop antenna called the Chameleon CHA RXL.
I’ve evaluated and reviewed a number of Chameleon’s ham radio antennas (primarily on QRPer.com). I find that the quality of their products are second to none. Price-wise, they tend to be at the top of the market, but keep in mind they machine and manufacture all of their antennas here in the US and they’re incredibly rugged; indeed, military-grade. And in the spirit of full disclosure, I’m proud Chameleon has been a sponsor the SWLing Post and QRPer.com since last year. My sponsors are by invite only and focus on companies I trust with our radio community’s business.
When Chameleon shipped the CHA RXL to me, it wasn’t from their factory, it was directly from the field: Fort Irwin, to be exact.
(Source: NTC Operations Group, Ft. Irwin)
This CHA RXL sample had been used by NTC Operations Group Fort Irwin (who, incidentally, won QRPX this year–click here to read the PDF report).
I was told that the condition of the antenna could be very rough after the QRPX because it had essentially been sandblasted in the desert winds. I was also told that someone accidently transmitted 5 watts into it at some point but it didn’t seem to harm it (for the record, like all amplified receive-only loops, it’s not designed to take RF).
Tony (W0NTC), who was one of the Ft. Irwin radio ops, sent me this note as he dropped off the shipment at Fort Irwin’s FedEx:
“Had a blast with [the CHA RXL], and it was absolutely critical while I was operating in the Army HF Low Power Competition (think tons of high powered MARS stations piling up and drowning out the 20W or less competitors). It absolutely crushed some localized RFI from a huge building I operated behind, and the receive on it I can only describe as “layered” in that I could hear stations somewhat clearer than usual if they transmitted simultaneously. Receiver I used was the IC-705 with default Auto Notch and Noise Reduction.”
Tony volunteered all of this info–I never asked him how it performed.
A few days later, I wasn’t sure what to expect when I opened the box although I knew that my operating locations were nowhere near as cool as its position next to a Humvee at Fort Irwin in the photo above!
I pulled the CHA RXL out of the box and it looked cosmetically flawless to me.
Frankly, there’s not a lot to get damaged. The 36 inch diameter loop is made of rigid aluminum and has a Navy gray powder coating. The preamplifier unit is completely sealed and made of a high-impact plastic/PVC type material. The steel loop is attached to the preamplifier loop flanges with wing nut connectors.
The only potentially vulnerable part of the antenna system is the Bias-T box which would normally be located in your shack close to your receiver.
If I mounted the CHA RXL permanently outdoors, I would use Coax Seal around the BNC connection point, of course.
Although the CHA RXL has a supplied mounting bracket for permanent installations, I love the fact that the preamp box has a 1/4” x 20 threaded camera socket on the bottom. This makes for a brilliant portable loop because it can so easily be mounted on a standard heavier-weight tripod! All antenna manufacturers should give us tripod mount options when possible.
On the air
One of the reasons amplified receive loop antennas have become so incredibly popular over the past couple of decades is because they do an amazing job mitigating radio frequency interference (RFI) a.k.a. “QRM.” If you live in a neighborhood with significant radio interference, you really should consider some form of loop in your antenna arsenal.
Ironically, at home, I live in pretty much an RFI-free zone. I’m surrounded by tens of thousands of acres of national forest, so I’ve only used amplified loop antennas in the past for mediumwave DXing–mainly, when I wanted to take advantage of their amazing ability to null out unwanted signals.
Many years ago, I purchased a Pixel Loop Pro antenna (now under a different name via DX Engineering), mounted it outside where it lasted almost a year before a bear decided to pull it down and chew through the coaxial feedline. He/she did so with enough energy that it ripped down the loop and damaged the connector end of the Pixel’s pre-amp. This all happened when our family was travelling for two months in Canada. Why bear, why?!? But I digress…
The CHA RXL version I was shipped has one single rigid loop–the “EU” version’s loop comes in two pieces (for easier shipping/transport)–but I had no problem fitting the entire assembled loop in the back seat of my Subaru or my truck (as long as no one was sitting back there at the time). If you plan to travel with your loop a lot, consider the “EU” version!
I’ve taken the CHA RXL to my parent’s home a couple of times and enjoyed doing a little mediumwave and shortwave listening. Inside the house, the loop would attenuate RFI nicely, but when outside it would all but eliminate many sources of RFI.
At their house, I primarily used my Icom IC-705 for cruising the bands (being careful, of course, to disengage the transmit function).
Listening time in my hometown, though, was very limited. Since the CHA RXL is so portable, I decided to set it up at home on our porch for a few days, giving me an opportunity to test both the Sangean ATS-909X2 and Tecsun H-501x with an external antenna.
I’ve especially appreciated using the CHA RXL on mediumwave. Even from our screened-in porch, I can rotate the loop and use its excellent nulling properties to pick out multiple station IDs on crowded frequencies.
I’ve spent time on shortwave, too, and found that it certainly gave these two portables a signal boost.
In fact, it was by using the CHA RXL that I discovered the audio level difference between AM and SSB on my ATS-909X2 is very minimal when an external antenna is connected.
I’m sure you’ll hear the CHA RXL in action when I post audio clips and recordings in upcoming reviews.
Summary
If I owned a CHA RXL loop, one of the first things I’d do is build a power cord for it with an in-line fuse and terminated with an Anderson Powerpole connector. Since the operating voltage of the Bias-T is 12-14 VDC, it would pair perfectly with one of my Bioenno LiFePo4 batteries, offering a power source with longevity in the field–ideal for a group LW/MW/SWL DXpedition.
It’s difficult for me to truly comment on the loop’s performance because I don’t have another loop at present for comparison. I can say that it’s amazing on mediumwave, where I’ve spent much of my listening time this past week. I believe shortwave reception has been at least on par with my former Pixel Loop, if not better. It’s hard to say, in truth, because propagation conditions have been so poor lately. The CHA RXL loop does effectively mitigate noise!
I’m not sure if the CHA RXL is currently on backorder or not, but I would suggest you check out the product page on Chameleon’s website and possibly contact them if you’re interested. They’ve a number of options and accessories to consider.
One thing for sure: this must be one of the most rugged and durable RX loop antennas on the market. In addition, that Navy gray powder coating helps this rigid aluminum loop disappear against the sky. I believe you could strategically mount this loop and the friendly neighborhood association may never notice–it’s pretty stealthy. Speaking of which…
Josh’s CHA RXL install and demo video
Josh over at Ham Radio Crash Course recently installed a CHA RXL on his house and tested it on several bands, comparing it with a number of his external antennas:
Anon-Co just announced that Tecsun has released their new portable, active loop antenna – the AN-48x (27.99 plus shipping) – and it is available for purchase. Copied below is their announcement:
Tecsun has launched its latest antenna which is now available at Anon-Co! This active loop antenna has a portable design and aims to enhance AM (LW, MW, SW) frequencies. The antenna comes with three types of connector cable and a ferrite coupler for connecting to different types of radios.
Personally, I like my TG34 (DE31MS equivalent). Though I have *no* experience with this model – as it is new – this is the type of antenna users either love or hate. My TG34 and the equivalents will amplify everything, including noise, but it has helped me make inaudible or barely audible signals audible. It’s inexpensive, portable, easy to deploy and store (great for travel) – but it’s really geared towards the SWL hobbyist who can’t invest in, or erect, something bigger and/or more expensive.
The biggest advantage that I can see with this new model: the antenna has three types of connections including BNC & RCA sockets.
It’s been a while since I posted a video on my YouTube Channel (but I’ve gotten the urge to make several more videos as I’ve been recently comparing my equipment – 16 portable receivers & many antennas).
I try to tune in to Radio Prague via WRMI on many weekday East Coast USA mornings from 1300-1325 UTC. Yesterday I encountered bad propagation but today was much better. The video linked to this post is from today – 30JAN2019 recorded around 1310 UTC.
Without repeating the debate, just take a look at this one example. As stated, reception was pretty good today off the little whip – but – there is an improvement using an amplified antenna. My question: is there a difference between the two amplified antennas? And if so, is the difference worth the price?
My TG34 is a clone of the DE31MS – purchased from Tquchina Radio & Component (ebay user: Tao Qu … they used to have an eBay store “Sino Radios” if I recall, but they stopped selling on eBay when the Post started cracking down on shipment of batteries – I actually exchanged an email with a frustrated Tao Qu when they closed the store).
I paid about $21 if I recall for my TG34 (the DE31MS is available today on eBay for as little as $17.28). I paid over $100 for the Sony AN-LP1 (out of production now and can be listed for as high as $300 on eBay). So … $21 versus “over $100”. Is there a difference – and if so – is it 5x the difference – 5x better?!
You be the judge.
P.S. Just a quick slightly over 1-minute video recorded inside my house (sitting in my breakfast nook) … typically “okay” reception but not my usual Listening Post.
In my recent post, The truth about portable amplified shortwave antennas, I argue that small, portable amplified antennas are, by and large, ineffective. The post comments are interesting, however; many readers agree, and some tout the Sony ANT-LP1 as worthy, but Mike made the following comment about his amplified antenna:
The one active antenna that I have been pleased with is one I built myself. The design was by ON2NLT and uses a ferrite rod, so it is somewhat directional. Rotating the unit (it is very compact) often allows nulling out noise or interference. You have to be careful not to crank up the gain too much though, or you will amplify the noise floor. The link is here
In the past week, I have had no less than 3 email inquiries from readers regarding which amplified antenna to purchase for their portable shortwave radio. My short answer? None.
In my opinion, there’s one fatal flaw with amplified antennas: they amplify noise just as much as they do the signal you wish to hear.
The only portable amplified antenna I’ve had any results with is the Sony AN-LP1 (now only available in Japan), and I attribute this success mainly to the fact that a suction cup, mounted at the top of the loop, allows it to be mounted on a window. Even then, results are often only marginally better than with the telescopic whip.
There may have been a time when portable amplified antennas made sense–a time prior to noisy AC adapters, flat screen TVs, and other consumer electronics which spew RFI (Radio Frequency Interference), polluting our shortwave bands. Today, however, you’ll be disappointed with the results of one of these, particularly if you travel–turning on the amplified antenna in a hotel room will increase the noise you hear two-fold, while weak broadcasters will remain lost in the static.
The Sangean ANT-60 is inexpensive and vesatile
So what can you do to improve the performance of your portable while traveling or at home? I’m still a fan of the roll-up antenna; like the Sangean ANT-60. They’re inexpensive ($12 US), packable, and versatile–the clip on the end of the reel allows the antenna wire to be clipped to curtains and blinds. Place it near a window, or even hang it outside. Antennas love being outside–just take it down when not in use.
In lieu of buying a roll-up antenna, you could simply attach an alligator clip to the end of a 20′ (6 meters) length of wire. The alligator clip can then attach to the end of your telescopic antenna, and you now have the same properties of a roll-up antenna for pennies. This is possibly the most cost-effective way to improve the performance of your portable shortwave radio. One note of caution: don’t get too generous with the length of your antenna wire. Some portable radios lack a robust front-end and a wire that’s too long could actually overload the receiver. Some Grundig G5’s were even sensitive to static discharges over a wire antenna. If uncertain, I would not exceed 20 feet in length (6 meters).
An alligator clip offers serious bang-for buck–especially if you already have the parts lying around!
I’ll never forget: one of the first email questions I received on SWLing.com was from a fellow listener in Washington state who wanted to hear stations better on his Sony portable. I suggested the alligator clip/antenna wire. He wrote back enthusiastically, “This is the most cost-effective improvement I have ever made to anything!” He was so encouraged with the performance improvement, he invested in a tabletop and a proper outdoor antenna with grounding.
So, I urge you to try a roll-up antenna or the alligator clip antenna before you waste money on a portable amplified antenna. Just my two cents.
Spread the radio love
Please support this website by adding us to your whitelist in your ad blocker. Ads are what helps us bring you premium content! Thank you!
